Metal dihydrocarbyl-dithiophosphyl-dithiophosphates their manufacture and use as additives for lubricants

ABSTRACT

The invention relates to compounds of the metal dihydrocarbyl-dithiophosphyl-dithiophosphate type, their manufacture and use. These compounds can be represented by the general formula: ##STR1## wherein R is a monovalent substantially hydrocarbon-containing radical of 1 to 30 carbon atoms, X and Y are each a hydrogen atom or a monovalent substantially hydrocarbon-containing radical of 1 to 30 carbon atoms, M is a metal selected from zinc, cadmium, lead and antimony or an oxygen- and/or sulfur-containing molybdenum complex, and n is the valence of said metal M. The compounds according to the invention can be used as additives for lubricants wherein they act as a very efficient wear preventive.

The present invention concerns compounds of the metaldihydrocarbyldithiophosphyl-dithiophosphate type, useful mainly asantioxidants, antiwear, extreme-pressure and anticorrosive additives forlubricating oils. It also concerns a process for manufacturing thesecompounds and the lubricants containing the same.

BACKGROUND OF THE INVENTION

The metal dialkyl- and diaryl-dithiophosphates, particularly thosecontaining zinc, have been widely used for many years to protect metalsurfaces under friction against wear and corrosion, as well as toprotect lubricating oils containing the same from oxidation. Details ofmanufacture of such additives are disclosed for example in U.S. Pat.Nos. 2,364,283--2,364,284,--2,365,938,--2,410,650,--2,438,876 and3,190,833. The metal dialkyl- and dialkylaryl-dithiophosphates disclosedin the prior art are generally characterized by Metal/P/S atomicproportions of 1/2/4--although the sulfur proportion may be higher asthe result of a further sulfurization, as described for example in U.S.Pat. No. 2,438,876. An efficient protection against wear requires theuse of such products in lubricating oils in proportions by weightgenerally ranging from 0.5 to 1.5%. On the other hand, German patent No.948,156 teaches that it is possible to obtain thiolthionophosphoric acidderivatives by reacting a thiolthionophosphoric (or dithiophosphoric)acid diester with ethylene oxide to form a triester ofthiolthionophosphoric acid with an oxygenated group, and then treatingsaid product with phosphorus pentasulfide. Although these derivativesare indicated as being liable to form salts with various metals (alkali,alkaline-earth, heavy metals) or with amines, only the preparation of anoleylamine salt is effectively disclosed.

SUMMARY OF THE INVENTION

One object of the invention is to provide new compounds of metaldithiophosphate type, providing particularly protection against wearsimilar to that achieved with additives of the prior art, but atsubstantially lower concentrations, or giving better protection at equalconcentration. Metal dihydrocarbyl-dithiophosphyl-dithiophosphatesaccording to the invention are complex compounds which can berepresented by the general formula (1) ##STR2## wherein R is amonovalent radical containing substantially hydrocarbons (or a mixtureof monovalent radicals containing substantially hydrocarbons) havingfrom 1 to 30 carbon atoms. X and Y each represent a hydrogen atom or amonovalent radical containing substantially hydrocarbons having 1 to 30carbon atoms, optionally further containing one or more heteroatoms(such for example as oxygen, nitrogen or halogen, etc . . . ); M is ametal selected from zinc, cadmium, lead, antimony or an oxygen- and/orsulfur-containing molybdenum complex group (hereinafter considered asequivalent to metal M), zinc being preferred; n is the valence of themetal M. R radicals may be aliphatic, arylaliphatic, alicyclic, aromaticor alkylaromatic and optionally contain one or more heteroatoms, such asoxygen, nitrogen, sulfur, phosphorus, halogen, etc . . . . The R radical(or a mixture of R radicals) generally originates from monohydroxylatedcompounds such as monoalcohols or monophenols, substituted orunsubstituted, examples of which will be given hereinafter. The natureof X and Y depends on the epoxide reactant ##STR3## used for thesynthesis of the products according to the invention, as hereinafterdescribed.

X and Y may represent, for example, a hydrogen atom or a methyl,chloromethyl or ethyl group; X and Y may also be interconnected and forma poly-methylene chain, for example with four CH₂ groups; X and Y mayfurther be longer hydrocarbon chains, for example octyl chains orhydrocarbon chains bearing functional groups such as ester groups, forexample alkyl octanoate (more particularly octyl octanoate). When metalM is a divalent metal, the respective atomic proportions of metal, ofphosphorus and of sulfur in the compounds of the invention are about1/6/12.

The metal dithiophosphates according to the invention may be prepared bya process comprising the following steps: A first step (a), wherein aso-called "first generation" dithiophosphoric acid is first prepared, byreaction between a hydroxylated compound (substituted or unsubstitutedalcohol or phenol) and phosphorus pentasulfide.

The reaction may be represented by the following equation: ##STR4##wherein R is defined as precedingly.

Examples of hydroxylated compounds to be used are aliphatic saturated orunsaturated monoalcohols such as methanol, ethanol, propanols, butanols,pentanols, hexanols, heptanols, octanols, nonanols; mixtures ofmonoalcohols of natural origin (e.g. fusel oil) or of synthetic origin(e.g. alcohols produced by the ALFOL process); alicyclic monoalcoholssuch as cyclohexanol; halides of aliphatic, alicyclic oraromatic-aliphatic monoalcohols such as, for example, 2-chloro- and2-bromo-ethanols, chloro- and bromo-propanols, butanols, pentanols, etc. . . ; chloro- or bromo-benzyl alcohols, chloro- or bromo-phenylethylalcohols.

Further examples are (poly-) alkoxy monoalcohols such for example as(poly-) methoxy-, ethoxy-, propoxy-, butoxy-, phenoxy-, alkylphenoxy-,ethanols and propanols, as well as their halogenated derivatives, andaromatic hydroxylated compounds such as phenol and its substitutedderivatives.

It must be understood that, in said step, two or more of the so-definedhydroxylated compounds can be used in admixture. The reaction of the oneor more hydroxylated compounds with phosphorus pentasulfide is generallyachieved as in the prior art, i,e. at temperatures ranging from 20° to180° C., preferably from 50° to 150° C., the reactants being used inproportions corresponding to stoichiometric or close thereto. In asecond step (b), product (II), obtained in step (a), is reacted with acompound having an epoxide group, such for example as ethylene,propylene, chloropropylene, butylene or cyclohexene oxide or still anoxide of fatty acid ester, particularly an alkyl (e.g. octyl)epoxystearate. Preferably ethylene and propylene oxides are used.

The reaction may be represented by the following equation 2; ##STR5##wherein R, X and Y are defined as precedingly.

This is a β-hydroxyalkylation reaction of the compound of formula (II),producing a hydroxylated compound of formula (III) which is adithiophosphoric alcohol.

This reaction is generally conducted at temperatures ranging from 0° to150° C., preferably from 20° to 130° C., the reactants being used inproportions corresponding to stoichiometric or close thereto.

In a third step (c), the dithiophosphoric alcohol (III) is reacted withphosphorus pentasulfide, according to a reaction scheme which can berepresented by the following equation (3): ##STR6## wherein R, X and Yare defined as precedingly. There is obtained a so-called "secondgeneration" dithiophosphyl dithiophosphoric acid (formula IV).

The reaction is perfomed at temperatures generally ranging from 20° to120° C., preferably from 40° to 90° C., the relative reactants amountsbeing close to stoichiometric.

In a fourth step (d), the dithiophosphoric acid (IV) is reacted, asalkali metal salt or ammonium salt, with a salt of metal M desired forthe final product. The reaction may be represented by the followingequation (4): ##STR7## wherein R, S, Y, M and n are defined asprecedingly. M₁ is an alkali metal or ammonium, Z is one equivalent ofthe anion of the MZ_(n) salt. Thus, Z may be a halogen (chlorine orbromine) atom, a nitrate or carboxylate (acetate, formate . . . ) group,or a carbonate, sulfate etc . . . half-group.

The operation is generally conducted in aqueous medium at temperaturesranging from 0° to 100° C., preferably from 40° to 60° C., the MZ_(n)metal salt being used in excess.

According to a second mode of synthesis of the products of theinvention, product (III), obtained in step (b) (dithiophosphoricalcohol), may be directly reacted with phosphorus pentasulfide, in thepresence of an oxide or hydroxide of the desired metal M, to give thedesired metal dihydrocarbyl-dithiophosphyl-dithiophosphate, complyingwith the general formula: ##STR8## metal M optionally being, asprecedingly, selected from zinc, cadmium, lead, antimony and molybdenumoxygenated and or sulfurized complex groups. In this reaction, hydrogensulfide and water are also formed.

The reaction is generally conducted between 40° and 100° C., preferablybetween 60° and 90° C., in the presence of a solvent used to remove theformed water by azeotropic stripping, the preferred solvent beingbenzene.

The products of the invention, which may be described as metaldihydrocarbyl-dithiophosphyl-dithiophosphates, may advantageously beused as additives for inorganic and/or synthetic lubricants,particularly for the protection of metal parts against wear andcorrosion and for the protection of lubricants against oxidation. Theseadditives may be used at concentrations by weight generally ranging from0.05 to 2%, but their main advantage is their high anti-wear activitymaking them satisfactorily efficient at concentrations ranging from 0.05to 1%.

EXAMPLES

The following examples illustrate the invention but must not beconsidered in any way as limiting the scope thereof. Example 10 is givenby way of comparison.

EXAMPLE 1

In a reactor of 5 liters capacity, provided with a stirrer and purgedwith nitrogen, 2210 g of 2-butanol (29.8 moles) are introduced. Thetemperature of the alcohol is brought to about 90° C. by externalheating means and then, by means of a feeding device for powderedreactants, 1490 g of P₂ S₅ (6.7 moles) are introduced in two hours intothe stirred alcohol while maintaining the reaction temperature between90° and 95° C.; then the reaction is continued for two additional hoursat a temperature from 95° to 100° C. so as to complete the P₂ S₅reaction.

A nitrogen stream is then supplied within the dialkyldithiophosphoricacid (of first generation) for 0.5 hour at 95°-100° C. so as to removedissolved hydrogen sulfide and the acid is cooled to 25°-30° C. By meansof a bromine funnel connected to the reactor, 810 g of propylene oxide(13,95 moles) are introduced into the acid in one hour, whilemaintaining the reaction temperature between 30° and 35° C.

The reactor is then subjected to a vacuum of 2666 Pa, whilesimultaneously heating the obtained thiophosphoric alcohol to 100° C.;in these conditions the 2-butanol and propylene oxide excesses areremoved by distillation. After cooling, 25 g of filtration earth(diatomaceous) are added and, after filtration, 3375 g of thiophosphoricalcohol are recovered.

In a second reactor of one liter capacity, provided with a stirrer andpurged with nitrogen, 240 g of the previously obtained thiophosphoricalcohol (0.8 mole) are introduced and the temperature is increased to95° C.

By means of a powder feeding device, 37 g (0.166 mole) of P₂ S₅ areprogressively added under stirring in 2 hours, while maintaining thetemperature at about 95° C. After cooling and filtration under inertatmosphere in the presence of diatomaceous earth, 209 g of secondgeneration acid (acidity=1.556×10⁻³ acid equivalent/g) are recovered.

This acid is neutralized with a solution of 13 g of sodium hydroxide in300 cc of water. The obtained milky solution is extracted with threetimes 500 cc of hexane to remove the excess of thiophosphoric alcoholand a portion of the partly soluble sodium salt, of the acid.

The aqueous solution (lower fraction), containing the purified sodiumsalt of the acid, is treated for 3 hours under stirring with a solutionof 60 g of heptahydrated zinc sulfate ZnSO₄, 7H₂ O (0.21 mole) in 150 ccof water.

The obtained milky suspension is extracted with three times 300 cc ofbenzene, the collected benzene extract is washed with water, dried overanhydrous sodium sulfate, filtered on diatomaceous earth and thenevaporated at 100° C. under reduced pressure up to constant weight.

90 g of a translucent very viscous organic product are obtained, whoseelementary analysis (Table 1) and RMN 13C, 1H analyses confirm thestructure, as well as the infra-red analysis which shows characteristicabsorption bands of zinc dialkyldithiophosphates, particularly at 970cm⁻¹ (attributable to P--O--C groups deriving from secondary alcohols),at 665 cm⁻¹ (attributable to P=S groups) and at 545 cm⁻¹ (attributableto P--S groups) and at 545 cm⁻¹ (attributable to P--S groups) theseabsorption bands appear to be substantially more intense than those ofthe corresponding conventional zinc di-sec-butyl dithiophosphate,particularly for P=S and P--S bands.

The product obtained complies with the formula: ##STR9##

EXAMPLE 2

The experiment of example 1 is repeated by reacting the aqueous solutionof the purified sodium salf of "second generation" dithiophosphoric acidprepared from 240 g of thiophosphoric alcohol, with 79.6 g oftrihydrated lead acetate Pb(OOCH₃)₂,3H₂ O dissolved in 150 cc of water.After treatment, about 100 g of organic product are recovered whoseelemental analysis (Table 1), RMN 13C, 1H and infra-red analyses confirmthe structure complying with the formula: ##STR10##

EXAMPLE 3

The experiment of example 2 is repeated by reacting 56 g of dihydratedcadmium acetate Cd(OOCCH₃)₂, 2H₂ O (0.21 mole); 80 g of product arerecovered whose elemental analysis (Table 1), RMN 13C, 1H and infra-redanalyses confirm the structure, complying with the formula: ##STR11##

                                      TABLE 1                                     __________________________________________________________________________                  % WEIGHT                                                         EXAMPLE PRODUCT OF                                                                    ##STR12##                                                                          THEORYFOUND CHSPMETALCHS*P**METAL***                                                                              METAL/P/S IN ATOMS                                                            theoryfound                 __________________________________________________________________________    1       Zn    36.36                                                                            6.66                                                                             26.48                                                                            12.79                                                                             4.50                                                                              36.65                                                                            6.59                                                                             27.02                                                                            12.40                                                                             4.47        1/5.85/12.32          2       Pb    33.13                                                                            6.07                                                                             24.12                                                                            11.65                                                                            12.99                                                                              33.8                                                                             6.24                                                                             23.84                                                                            11.20                                                                            12.40   1/6/12                                                                             1/6.04/12.42          3       Cd    35.22                                                                            6.45                                                                             25.65                                                                            12.30                                                                             7.49                                                                              35.84                                                                            6.65                                                                             25.34                                                                            12.20                                                                             7.20        1/6.15/12.34          __________________________________________________________________________     *determination by LECO methode                                                **determination by X fluorescence                                             ***determination by EDTA complexometry                                   

EXAMPLE 4

In a reactor of one liter capacity, equipped with a stirrer, aDEAN-STARK separator with cooler and a feeding system for powderedreactants, 200 g (0.66 mole) of the thiophosphoric alcohol prepared inexample 1, 300 cc of benzene and 20.3 g (0.25 mole) of ZnO, areintroduced under an inert atmosphere.

The obtained suspension is heated under stirring up to benzene reflux;the temperature of the medium ranges from 85° to 90° C.

By means of the system for feeding powdered reactants, 36.7 g (0.165mole) of P₂ S₅ are progressively added in 3 hours. Resultant "secondgeneration" acid reacts with ZnO; the water produced by the reaction isremoved, as it is formed, by azeotropic stripping in a DEAN-STARKseparator. The mixture is maintained for 3 additional hours at refluxand then allowed to cool.

The benzene solution is then filtered, in the presence of diatomaceousearth, then evaporated at 100° C. under reduced pressure up to constantweight.

225 g of a viscous product are thus recovered, whose elemental analysis(Table II), RMN 13C, 1H and infra-red analyses confirm the structure,corresponding to the formula: ##STR13##

EXAMPLE 5

The experiment of example 4 is repeated with the use of 224.4 g (2.2moles) OF 4-methyl 2-pentanol and of 11.1 g (0.5 mole) of P₂ S₅ ; thetemperature of formation of the "first generation" acid is 85°-90° C.

After removal of the dissolved H₂ S, by bubbling of a nitrogen stream,the acid is converted to thiophosphoric alcohol by addition, at 30°-35°C., of 60.9 g (1.05 mole) of propylene oxide. The alcohol and propyleneoxide excesses are removed by heating at 100° C. under reduced pressure.

Then 400 cc of benzene and 25 g (0.31 mole) of ZnO are added and themixture is brought to reflux (87°-90° C.) under stirring. Then, 53.3 g(0.24 mole) of P₂ S₅ are progressively added in 3 hours; the waterproduced in the reaction being progressively carried away by theheteroazeotropic effect of the solvent.

After 3 further hours of reflux, filtration and evaporation 367 g of aviscous translucent product are obtained whose elemental analysis (TableII), RMN 13C, 1H and infra-red analyses confirm the structure,corresponding to the formula: ##STR14##

EXAMPLE 6

The experiment of example 4 is repeated with the use of 286 g (2.2moles) of 2-octanol, 111.1 g (0.5 mole) of P₂ S₅ and 60.9 g (1.05 mole)of propylene oxide. The temperature at which the "first generation" acidforms is between 115° and 120° C.

After removal of the excess reactants and of dissolved H₂ S, the mixtureis allowed to cool and then 400 cc of benzene and 25 g (0.31 mole) ofZnO are added and the mixture is brought to reflux. Then 52.7 g (0.237mole) of P₂ S₅ are added in 3 hours, and the reaction is continued for 4additional hours, the reaction water being removed continuously.

After cooling, filtration on diatomaceous earth and evaporation underreduced pressure, 432 g of a translucent viscous product are recoveredwhose elemental analysis (table II), RMN 13C, 1H and infra-red analysesconfirm the structure, corresponding to the formula: ##STR15##

EXAMPLE 7

The experiment of example 5 is repeated with the use of 262.44 g (1mole) of dodecylphenol and 52.78 g (0.2375 mole) of P₂ S₅ ; thetemperature of formation of the "first generation" dithiophosphoric acidis 145°-155° C.

After removal of the dissolved H₂ S, by nitrogen bubbling, the acid isconverted to thiophosphoric alcohol by addition, at 30°-35° C., of 28.93g (0.5 mole) of propylene oxide. The excess of propylene oxide isremoved by heating at 100° C. under reduced pressure.

Then 400 cc of benzene and 38.7 g of ZnO (0.475 mole) are added to themixture which is then brought to reflux.

Then 7.23 g of P₂ S₅ (0.119 mole) are progressively introduced in 3hours; the water produced in the reaction is continuously removed byheteroazeotropic stripping.

After 3 additional hours of reflux, filtration through diatomaceousearth and evaporation under reduced pressure, 332 g of product arerecovered whose elemental analysis (Table II), RMN 13C, 1H and infra-redanalyses, confirm the structure, corresponding to the formula: ##STR16##

EXAMPLE 8

The experiment of example 4 is repeated with the use of a mixture of81.4 g (1.1 mole) of n-butanol, 143 g (1.1 mole) of 2-octanol, 111.1 g(0.5 mole) of P₂ S₅, 60.9 g (1.05 mole) of propylene oxide and 25 g(0.31 mole) of ZnO; the temperature of formation of the "firstgeneration" acid is 115° C. The preparation of the desired product iscontinued in the conditions of example 6.

325 g of translucent, viscous product are recovered, whose elementalanalysis (Table II), RMN 13C, 1H and infra-red analyses confirm thestructure, corresponding to the formula: ##STR17## this formula being anoverall formula representative of a mixture of products containingsimilar proportions of groups derived from n-butanol and from 2-octanol.

    __________________________________________________________________________     ##STR18##                                                                                          % WEIGHT                      Zn/P/S                    Product of            Theory         Found          in atoms                  Example                                                                             RO              C  H  S  P  Zn C  H  S  P  Zn Theory                                                                            Found                 __________________________________________________________________________           ##STR19##      36.36                                                                            6.66                                                                             26.48                                                                            12.79                                                                            4.50                                                                             36.71                                                                            6.92                                                                             26.8                                                                             12.20                                                                            4.30                                                                             1/6/12                                                                            1/6/12.7              5                                                                                    ##STR20##      42.96                                                                            7.69                                                                             22.94                                                                            11.08                                                                            3.90                                                                             43.15                                                                            8.10                                                                             23.5                                                                             10.74                                                                            3.76                                                                             1/6/12                                                                            1/5.82/12.7           6                                                                                    ##STR21##      47.99                                                                            8.48                                                                             20.23                                                                            9.77                                                                             3.44                                                                             48.50                                                                            8.62                                                                             19.62                                                                            9.40                                                                             3.20                                                                             1/6/12                                                                            1/6.2/12.5            7                                                                                    ##STR22##      63.31                                                                            8.72                                                                             13.00                                                                            6.28                                                                             2.21                                                                             64.1                                                                             8.70                                                                             12.30                                                                            6.10                                                                             2.17                                                                             1/6/12                                                                            1/5.93/11.5           8                                                                                    ##STR23##      42.96                                                                            7.69                                                                             22.94                                                                            11.08                                                                            3.90                                                                             43.27                                                                            7.98                                                                             23.3                                                                             10.89                                                                            3.82                                                                             1/6/12                                                                            1/6.02/12.43          __________________________________________________________________________

EXAMPLE 9

The experiment of example 7 is repeated, except that propylene oxide isreplaced with the same molar amount of ethylene oxide. At the end of theexperiment, 314 g of product are recovered, whose elemental analysis isas follows:

    ______________________________________                                                      % WEIGHT                                                        ELEMENT         THEORY    FOUND                                               ______________________________________                                        C               62.88     64.31                                               H               8.61      8.70                                                S               13.25     13.4                                                P               6.40      6.1                                                 Zn              2.25      2.28                                                Zn/P/S          1/6/12    1/5.64/12                                           in atoms                                                                      ______________________________________                                    

The RMN 13C, 1H and infra-red analyses confirm the structurecorresponding to the formula: ##STR24##

EXAMPLE 10 (comparative)

An amine salt corresponding to the teaching of German patent 948,156 hasalso been prepared as follows:

In a reactor of 0.5 liter, 100 g of a so-called "second generation" acidare prepared (acidity=1.556×10⁻³ acid eq./g) according to the methoddescribed in example 1.

41.6 g of oleylamine, i.e. the stoichiometric amount required forneutralizing the acid, are added. After exothermic reaction, the mixtureis heated for 3 hours to complete the reaction.

After filtration, 127 g of product are recovered whose elementalanalysis indicates the following P, S and N contents.

    ______________________________________                                                       Found Theory                                                   ______________________________________                                        P % weight       9.25    9.66                                                 S % weight       20.52   20.00                                                N % weight       1.45    1.46                                                 ______________________________________                                    

This confirms the structure of the oleylamine salt, which may berepresented by the formula: ##STR25##

EXAMPLE 11 Tests

The anti-wear properties of the additives prepared according to thepreceding examples have geen evidenced by means of an XL 5 PEUGEOTengine with overhead camshaft.

The arrangement used for the tests consists of two cylinder heads of anXL 5 PEUGEOT engine mounted on supports adapted for an oil circulationthrough the system. The camshafts are driven directly at their end bytwo-speed electric motors. An oil pump system is provided to reconstructthe normal conditions of a complete engine, as well as thepressurization of the circuit before actuation of the camshafts.

A fine filtration (substantially 10 μm) provides for the removal of mostof the particles formed by friction.

The main test conditions are as follows:

running speed:

1 minute at 750 r.p.m.

2 minutes at 1500 r.p.m.

operating time: 50 hours

oil temperature: 50° C.

feeding pressure of the valve rockers: 2 bars at 50° C.

charge of the springs at maximum lifting: 1200N

intermediary clearance adjustment at 25 hours

application of pressure and temperature to camshafts before starting thedriving engines.

The anti-wear properties of the additives are evaluated by averaging thewear of the valve rockers after test (average wear of the 16 valverockers).

The lubricating oil consists of a 175 Neutral solvent mineral oil,containing:

3.35% by weight of detergent additive (Ca=1800 ppm)

5% by weight of ashless dispersing additive.

Three series of experiments have been conducted, one with the use ofzinc dithiophosphate of example 1 (Zn/P/S=1/5.85/12.32), a second one bymeans of the oleylamine salt of example 10 and a third one by means ofthe conventional zinc dithiophosphate obtained from 2-butanol(Zn/P/S=1/2/4/); the results are summarized in Table III hereinafter:

                                      TABLE III                                   __________________________________________________________________________    ADDITIVE                                                                                                         Additive       *                                                              in oil                                                                              Zn in oil                                                                          P in oil                                                                          Average wear of valve       NATURE                             (weight %)                                                                          (ppm)                                                                              (ppm)                                                                             rockers mg/valve            __________________________________________________________________________                                                      rocker                      NONE                               0       0    0 **                           ##STR26##                         1.174 0.782 0.391 0.293                                                             1400 933 466 350                                                                   1326 884 442 331                                                                  14.7 15.6 17.0 26.2         conventional                                                                   ##STR27##                         1.433 0.956                                                                           0 0                                                                              1326 884                                                                          23.7 28.0                   of example 10                                                                  ##STR28##                         1.069 0.713 0.260 0.130                                                              478 319 116 58                                                                    1326 884 322 161                                                                  12.9 13.5 13.2 14.1         of example 1                                                                  __________________________________________________________________________     *average wear calculated on 16 valve rockers (8 by cylinderhead)              **destruction of the valve rockers after a few hours of test             

Table III shows a high anti-wear activity for one of the additivesaccording to the invention as compared with the conventional zincdithiophosphate obtained from the same initial alcohol and with thereaction product between oleylamine and "second generation"dithiophosphoric acid.

As a matter of fact, it is observed that, for commercial dithiophosphateand for amine dithiophosphate, the protection of the valve rockersagainst wear continuously decreases with a decrease of the lubricantphosphorus content, particularly below about 1500 ppm of phosphorus,whereas on the contrary, with one of the products of the invention, thisprotection is achieved even at phosphorus contents as low as about 160ppm.

The same experiments, performed with identical molar amounts ofadditives of examples 2 to 9 give similar results.

What is claimed as the invention is:
 1. A compound of metaldihydrocarbyl-dithiophosphyl-dithiophosphate type, represented by thegeneral formula: ##STR29## wherein R is at least one monovalentsubstantially hydrocarbon-containing radical of 1 to 30 carbon atoms; Xand Y are each a hydrogen atom or a substantially hydrocarbon-containingradical of 1 to 30 carbon atoms and may be optionally interconnected toform a polymethylene chain, M is a metal selected from zinc, cadmiumlead and antimony; and n is the valence of the metal.
 2. A compoundaccording to claim 1, wherein R is at least one aliphatic,arylaliphatic, alicyclic, aromatic or alkyl-aromatic radical, derivedfrom an aliphatic or alicyclic monoalcohols or from a monophenol or amonophenol substituted by at least one alkyl group.
 3. A Compoundaccording to claim 1, wherein X and Y are each hydrogen, methyl,chloromethyl, ethyl, octyl or alkyl octanoate, or together form apolymethylene chain with four CH₂ groups.
 4. A compound according toclaim 1, wherein N is zinc.
 5. A compound according to claim 1, whereinmetal M is in a divalent state and the respective atomic proportions ofsaid metal M, of phosphorus and of sulfur in said compound are about1/6/12.
 6. A process for manufacturing a compound according to claim 1,comprising:(a) reacting a hydroxylated compound ROH with phosphoruspentasulfide to form a dithiophosphoric acid of the formula: ##STR30## Rbeing defined as in claim 1; (b) reacting the dithiophosphoric acidobtained in step (a) with a compound having an epoxide group ##STR31##to form a dithiophosphoric alcohol of the formula ##STR32## X and Ybeing defined as in claim 1; (c) reacting the dithiophosphoric alcoholobtained in step (b) with phosphorus pentasulfide to form adithiophosphyl-dithiophosphoric acid of the formula: ##STR33## and (d)reacting the dithiophosphyl-dithiophosphoric acid obtained in step (c)with a basic compound to obtain the alkali metal or ammonium salt, and(e) reacting the salt obtained in step (d) with a salt of metal M, toform the desired compound of the formula: ##STR34##
 7. A process formanufacturing a compound according to 1, characterized by the stepsof:(a) reacting a hydroxylated compound ROH with phosphorus pentasulfideto form a dithiophosphoric acid complying with the formula: ##STR35## Rbeing defined as in claim 1; (b) reacting the dithiophosphoric acidobtained in step (a) with a compound having an epoxide group ##STR36##to form a dithiophosphoric alcohol of the formula: ##STR37## X and Ybeing defined as in claim 1; and (c) reacting the dithiophosphoricalcohol obtained in step (b) with phosphorus pentasulfide in thepresence of an oxide or hydroxide of said metal M, to form the desiredcompound.
 8. A process according to claim 7, characterized in that step(c) is performed in the presence of a solvent adapted to remove theformed water by azeotropic stripping.
 9. A lubricating composition,comprising a major proportion of mineral or synthetic lubricating oiland a minor proportion from 0.05 to 2% by weight of at least onecompound according to claim
 1. 10. A composition according to claim 9,characterized in that said minor proportion is from 0.05 to 1% byweight.
 11. A compound according to claim 2, wherein the aliphatic,acylaliphatic, alicyclic, aromatic or alkylaromatic radical contains atleast one hetero atom.